Conventionally, a programmable logic controller (PLC) is used to sequentially control control-object apparatuses in manufacturing lines or individual devices in a factory or at sites such as plants and office buildings. In programming therefor, an FBD language, which is a programming language for the programmable logic controller defined as standard IEC61131-3 by the International Electrotechnical Commission (IEC), is used.
The program in FBD language describes a series of processes by arranging and connecting FBD parts such as a function or a function block. Each FBD part includes input terminals on the left side and output terminals on the right side, and FBD parts are connected via the input terminals and the output terminals.
In the connections of the FBD language, one connection line can be separated into a plurality of connections and a terminal can be made unconnected. Further, as a case in which a compilation error occurs in a created program, there are, for example, cases where data types of a source terminal and a destination terminal being connected are different and where a terminal that is required to be connected has not been connected.
Patent Literature 1 discloses an invention in which, when a connection is supplied to a designated part, all of the unconnected terminals are automatically connected to the terminals of a nearby FBD part from the topmost portion.